The present invention relates to aqueous ink containing a dye, especially aqueous ink suitable for an ink jet recording system, and a simple process for producing a dye.
Aqueous ink used in writing instruments or for recording of an ink jet recording system is basically made of a dye, water and an organic solvent. In consideration of an odor and safe to the human body and the surrounding environment, aqueous ink containing water as a main solvent has been in high demand, and acid dyes, direct dyes and the like which are soluble in water have been actually used. In this connection, various characteristics are required for dyes and aqueous ink.
Especially, with respect to aqueous ink used in a recording liquid of an ink jet recording system, the following various characteristics are required. However, all these characteristics have not been satisfied at present.
(1) Physical properties such as viscosity, surface tension, specific conductivity, density, pH and the like of ink are appropriate.
(2) Long-term storage stability of ink is good.
(3) Dissolution stability of a soluble component is high and clogging of a nozzle does not occur.
(4) Quick-drying property of a recording medium is good.
(5) A recorded image is sharp without blotting, and light fastness, water resistance and moisture resistance are good.
As stated above, characteristics of ink used in an ink jet recording system in particular are greatly influenced by characteristics inherent in a dye. It is thus quite important to produce a dye and aqueous ink that satisfy these conditions.
The invention aims to provide aqueous ink which has a high image quality without blotting, which is excellent in storage stability, light fastness, moisture resistance and jet stability and which is useful as a recording liquid of an ink jet recording system.
The present inventors have assiduously conducted investigations to solve these problems, and have consequently come to complete the invention.
That is, the invention relates to:
(1) aqueous ink for ink jet recording comprising a coloring matter and an aqueous medium as main components, in which at least one of dyes represented by the formula (A) or their salts is contained as the coloring matter. 
xe2x80x83[wherein R1 and R3, independently from each other, represent a hydrogen atom, a hydroxyl group or a halogen atom, R2 and R4, independently from each other, represent a hydrogen atom, an optionally substituted alkyl group, an optionally substituted aryl group or an optionally substituted aralkyl group, A represents a phenyl group or a naphthyl group (the phenyl group or the naphthyl group may be substituted with any of a halogen atom, a hydroxyl group, an amino group, an optionally substituted alkyl group, an alkoxy group, a carboxyl group, a carboxylic acid ester group, a carboxylic acid amide group, a sulfonic acid group, a sulfonic acid amide group), X represents an alkylene group, a phenylene group, a xylylene group, a naphthylene group, a biphenylene group or a divalent bonding group represented by the formula (2) 
xe2x80x83in which Z represents xe2x80x94COxe2x80x94, xe2x80x94NHCONHxe2x80x94, xe2x80x94NHCSNHxe2x80x94 or formula (3) 
xe2x80x83(these bonding groups may be substituted with a halogen atom, an alkyl group, an alkoxy group, a hydroxyl group, an amino group, a carboxyl group or a sulfonic acid group), and m and n, independently from each other, represent an integer of 1 to 4].
(2) the aqueous ink for ink jet recording as recited in (1), wherein in the formula (A), at least one of R1 and R3 is a halogen atom,
(3) the aqueous ink for ink jet recording as recited in (1) or (2), wherein in the formula (A), X is an optionally substituted phenylene group,
(4) the aqueous ink for ink jet recording as recited in any of (1) to (3), wherein in the formula (A), A is a naphthyl group (the naphthyl group may be substituted with any of a halogen atom, a hydroxyl group, an amino group, an optionally substituted alkyl group, an alkoxy group, a carboxyl group, a carboxylic acid ester group, a carboxylic acid amide group, a sulfonic acid group and a sulfonic acid amide group),
(5) the aqueous ink for ink jet recording as recited in (1), wherein the dyes are dyes represented by the formula (B) 
xe2x80x83or their salts,
(6) aqueous ink for ink jet recording, wherein a dye contains at least one of the dyes represented by the formula (B) as recited in (5), other dyes represented by the formula (C) 
xe2x80x83[wherein R5 and R7, independently from each other, represent a hydrogen atom, an optionally substituted alkyl group, an optionally substituted alkoxy group, an amino group, analkylamino group, a hydroxyl group or a halogen atom, R6 and R8, independently from each other, represent a hydrogen atom, an optionally substituted alkyl group, an optionally substituted aryl group or an aralkyl group, A represents a phenyl group or a naphthyl group (the phenyl group or the naphthyl group may be substituted with any of a halogen atom, a hydroxyl group, an amino group, an optionally substituted alkyl group, an alkoxy group, a carboxyl group, a carboxylic acid ester group, a carboxylic acid amide group, a sulfonic acid group and a sulfonic acid amide group), X represents a divalent bonding group, and m1 and n1, independently from each other, represent an integer of 1 to 4] or their salts,
(7) a process for producing a dye, which comprises dissolving a dye represented by the formula (C) or its salt in water, and adjusting pH of the aqueous solution to 9 or more to remove insoluble matters formed. 
xe2x80x83[wherein R5 and R7, independently from each other, represent a hydrogen atom, an optionally substituted alkyl group, an optionally substituted alkoxy group, an amino group, an alkylamino group, a hydroxyl group or a halogen atom, R6 and R8, independently from each other, represent a hydrogen atom, an optionally substituted alkyl group, an optionally substituted aryl group or an aralkyl group, A represents a phenyl group or a naphthyl group (the phenyl group or the naphthyl group may be substituted with any of a halogen atom, a hydroxyl group, an amino group, an optionally substituted alkyl group, an alkoxy group, a carboxyl group, a carboxylic acid ester group, a carboxylic acid amide group, a sulfonic acid group and a sulfonic acid amide group), X represents a divalent bonding group, and m1 and n1, independently from each other, represent an integer of 1 to 4],
(8) a process for producing a dye, which comprises, after dissolving the dye represented by the formula (C) as recited in (7) or its salt in water to form the aqueous solution, mixing the aqueous solution with a water-soluble organic solvent to crystallize the dye,
(9) a process for producing a dye, which comprises mixing the aqueous solution obtained by dissolving the dye represented by the formula (C) as recited in (7) or its salt in water and adjusting pH of the aqueous solution to 9 or more to remove insoluble matters formed with a water-soluble organic solvent to crystallize the dye,
(10) the process for producing the dye as recited in any of (7) to (9), wherein in the formula (C), X is an alkylene group, a phenylene group, a xylylene group, a naphthylene group, a biphenylene group or a divalent bonding group represented by the formula (5) 
xe2x80x83in which Z represents an oxygen atom, a sulfur atom, xe2x80x94COxe2x80x94, xe2x80x94NHCONHxe2x80x94, xe2x80x94NHCSNHxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 or the formula (6) 
xe2x80x83(these bonding groups may be substituted with a halogen atom, an alkyl group, an alkoxy group, a hydroxyl group, an amino group, a carboxyl group or a sulfonic acid group),
(11) the process for producing the dye as recited in any of (7) to (9), wherein in the formula (C), X is an optionally substituted phenylene group,
(12) the process for producing the dye as recited in any of (7) to (9), wherein in the formula (C), A is a naphthyl group (the naphthyl group may be substituted with any of a halogen atom, a hydroxyl group, an amino group, an optionally substituted alkyl group, an alkoxy group, a carboxyl group, a carboxylic acid ester group, a carboxylic acid amide group, a sulfonic acid group and a sulfonic acid amide group),
(13) the process for producing the dye as recited in any of (7) to (9), wherein the dye is the formula (B), and
(14) aqueous ink for ink jet recording characterized by containing at least one of the dyes produced by the process for producing the dye as recited in any of (7) to (13).